Object.prototype.c = 3
let obj = {  // new Object()
  a: 1,
  b: {n: 2}
}
// let arr = [1, 2, 3]
// console.log(obj.c);

// for (let key in obj) {
//   console.log(key, obj[key]);
// }

console.log(obj.hasOwnProperty('c'));